Patients suffering lung failure, possibly from COVID-19 or hypoxic lung failure, will need life-saving support from a breathing machine. Any patient needing this support requires drugs to keep them sleepy, or "sedated" to be comfortable on this machine. Sedation is made possible by using drugs given through a vein. Unfortunately, these drugs are in short supply worldwide due to the high number of COVID-19 patients needing these machines.

Another way to provide sleep is by using gases that are breathed in. These are used every day in operating rooms to perform surgery. These gases, also called "inhaled agents" can also be used in intensive care units and may have several important benefits for patients and the hospital. Research shows they may reduce swelling in the lung and increase oxygen levels, which allows patients to recover faster and reduce the time spent on a breathing machine. In turn, this allows the breathing machine to be used again for the next sick patient. These drugs may also increase the number of patients who live through their illness. Inhaled agents are widely available and their use could dramatically lesson the pressure on limited drug supplies.

This research is a study being carried out in a number of hospitals that will compare how well patients recover from these illnesses depending on which type of sedation drug they receive. The plan is to evaluate the number who survive, their time spent on a breathing machine and time in the hospital. This study may show immediate benefits and may provide a cost effective and practical solution to the current challenges caring for patients and the hospital space, equipment and drugs to the greatest benefit. Furthermore, the study will be investigating inflammatory profile and neuro-cognitive profiles in ventilated patients. Finally, this trial will be a team of experts in sedation drugs who care for patients with proven or suspected COVID-19 who need lifesaving treatments.

Multicentre open-label, pragmatic, randomized controlled trial and a parallel prospective (non-randomized) cohort study conducted in ICUs and ICU enabled environments caring in critically ill COVID-19 and non-COVID hypoxic respiratory failure patients.

Participants will be mechanically ventilated and will be variably randomized, within 72 hours of start of sedation treatment, in a 1:1 ratio to either an intravenous or inhaled volatile-based sedation arm depending on availability of sedative drugs for both arms. Stratification will be done by:

1. Age ≥ 65 years
2. participating centre
3. PaO2/FiO2 ratio of 150

Patients who cannot be randomized (due to technical or resource issues in some areas of the hospital) will be entered into the parallel prospective (non-randomized) cohort study and will receive intravenous or inhaled sedation as able in their designated unit.

Sedation will be administered according to standard sedation practice and in keeping with current guidelines.

Participants will be followed:

• daily in ICU until 30 days after enrollment, ICU discharge or death, whichever occurs first;
• at 30 days after last dose of drug administration by telephone or through the hospital healthcare database;
• at 60 days, 90 days, and 365 days after enrollment by telephone and/or through data linkages with a provincial or hospital or state healthcare database;
• Participants will have the option to participate in the neuro-cognitive and / or biomarker assessments

Inclusion Criteria:

1. ≥ 18 years of age

2. Mechanically ventilated and expected to remain mechanically ventilated at the end of the next day

3. Receiving IV sedation by infusion or bolus for ≤72 hours to facilitate mechanical ventilation Transferred patients with escalating ventilation needs are eligible for recruitment within ≤72 hours of sedation commenced within the participating trial site that they were transferred to.

   Note: Intravenous sedation required to support mechanical ventilation includes use of one or more of the following agents: benzodiazepines, propofol, ketamine, barbiturates, alpha-2 agonist, opioids. Patients receiving intravenous opioids only i.e., fentanyl ≥ 50mcg/hour, hydromorphone ≥ 0.4mg/hour (or bolus q1h) for analgesia and sedation or agitation to assist mechanical ventilation are eligible for inclusion.

4. Mechanically ventilated patients +/- extracorporeal membrane oxygenation (extracorporeal life) support with:

   1. Proven or suspected (under investigation) COVID-19, or
   2. COVID-19 negative patients who have a PaO2FiO2 ratio ≤300 measured with arterial blood gas at least once during the 12 hours prior to enrollment.

Note: If arterial blood gas measurement is unavailable, the PaO2 can be imputed from the pulse oximetry measurement

Exclusion Criteria:

1. Contraindications to sedatives, such as propofol infusion syndrome or malignant hyperthermia;
2. Known allergy to any of the ingredients or components of the investigational products; sevoflurane or isoflurane;
3. Suspect or evidence of high intracranial pressure;
4. Severe brain injury that is likely to lead to sustained very low conscious levels or vegetative state
5. Severe neuromuscular disorder for example amyotrophic lateral sclerosis, Gullian Barre Syndrome that are the primary cause of needing ICU admission and mechanical ventilation
6. One-lung ventilation or pneumonectomy;
7. Ideal estimated tidal volume too low for delivery of inhaled agents. Target (6ml/kg) < 200ml;
8. Use of inhaled prostacyclin which is contraindicated in the presence of a miniature vaporizer (i.e., Anesthesia Conserving Device). This agent has a high viscosity that leads to poor vaporization of the volatile agent. Note: Other inhaled pulmonary vasodilators such as nitric oxide can be safely administered in the presence of miniature vaporizers. Use of prostacyclin is permissible with an anesthesia machine and MADM;
9. Known pregnancy
10. Moribund patient not expected to survive >12 hours